"I want to reassure the Australian people that it will be as long as it needs to be, but as short as it possibly can be.

"It is a dangerous mission, but I am confident that the CDF [Chief of the Defence Force] has put in place all possible measures to minimise risk."

Defence Force Chief Mark Binskin said the air strikes "won't be rushed" and would begin "over the coming days".

He said US led air strikes were having some success.

"We are seeing ISIL react to that and change their tactics. And to be honest with you, what air power does, it stops people being able to mass forces on the ground in a land campaign and that's exactly what we aim to do," he said.

Mr Abbott said while Australia was to begin "combat operations" against the IS targets, it was not "strictly accurate" to describe it as a war.

"We are not in combat against another country," he said.

"We are engaged in combat operations against an insurgency in support of the legitimate government of Iraq."

"Labor's support for this important development continues to be underpinned by our key principles which we've enunciated to the Parliament and we will continue to put the national security of our nation ahead of politics."

Retired major-general Jim Molan, who led Australian forces into the last Iraq war, on Friday predicted this would be the start of a long campaign.

"I see it happening fairly fast... [in] the next 24 hours we should see strikes occurring," he said.

"My understanding is that whatever will come out of today may not yet apply to the special forces on the ground somewhere in northern Iraq."

United States forces began strikes against IS targets in Iraq in August, and in Syria last month.

Greens leader Christine Milne said Mr Abbott was blindly following the United States into war.

"He didn't wait to consider Australia's national interest. He didn't have and doesn't have now a strategic plan for Australia's involvement," she said.